The present invention is directed to ink jet ink compositions. More specifically, the present invention is directed to ink compositions that are primarily suitable for ink jet printing processes and which contain linear N-hydroxyl substituted polyethylene imine polymers. The inks of the present invention are particularly preferred for use in continuous stream ink jet printing systems.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The second type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink-filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again.
Ink jet printers of the continuous stream type employ printheads having one or more orifices or nozzles from which continuous streams of ink droplets are emitted and directed toward a recording medium. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. Printing information is transferred to the droplets of each stream by electrodes that charge the passing droplets, which permits each droplet to be individually charged so that it may be positioned at a distinct location on the recording medium or sent to the gutter for recirculation. As the droplets proceed in flight from the charging electrodes toward the recording medium, they are passed through an electric field which deflects each individually charged droplet in accordance with its charge magnitude to specific pixel locations on the recording medium. The continuous stream ink jet printing process is described, for example, in U.S. Pat. Nos. 4,255,754; 4,698,123 and 4,751,517, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 4,789,400, the disclosure of which is totally incorporated herein by reference, discloses a waterfast ink jet composition which comprises a major amount of water, a hydroxypropylated polyethyleneimine with a weight average molecular weight of from about 1,000 to about 10,000, and a dye component, wherein the ink has a viscosity of from about 1 to about 5 centipoise.
Ink jet ink compositions are known, and generally contain water soluble dyes. For example, U.S. Pat. No. 3,846,141 discloses an ink jet ink which comprises an aqueous solution of a water soluble dye and a humectant material formed of a mixture of a lower alkoxy triglycol and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the ink viscosity is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the jet orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inch, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example paper, and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system.
In addition, U.S. Pat. No. 4,279,653 discloses ink jet inks containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet ink containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Further, U.S. Pat. No. 4,267,088 discloses coatings particularly useful as marking inks which contain an epichlorohydrin-modified polyethyleneimine and an ethylene oxide modified polyethyleneimine in an aqueous solution. Other patents of interest are U.S. Pat. Nos. 4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989; 4,299,630; 3,864,296; 4,238,234; 3,234,025; 4,520,143; 3,920,855; and 4,182,612.
Further, U.S. Pat. No. 4,197,135 discloses ink compositions with improved waterfastness comprising at least one water soluble dye and a polyamine with 7 or more nitrogen atoms per molecule. Specifically, this patent illustrates an ink composition comprising an aqueous solution of at least one water-soluble dye and from about 0.5 percent to about 10 percent by weight of a polyamine having 7 or more nitrogen atoms per molecule, wherein the composition has a pH of 8 or above. In column 1, beginning at line 61, the patent states that the preferred polyamines have the hydrogen of the primary amine group replaced with either a methyl or a hydroxyethyl group. Examples of fully substituted polyamines are outlined in column 2, beginning at line 40, of the '135 patent.
Additionally, U.S. Pat. No. 4,659,382, the disclosure of which is totally incorporated herein by reference, illustrates an ink composition with improved waterfastness useful for jet printing processes which comprises a major amount of water, a hydroxyethylated polyethyleneimine polymer, and a dye composition, wherein the polymer has incorporated therein from about 65 percent to about 80 percent of hydroxyethyl groups. A specific preferred ink composition illustrated in the aforementioned patent comprises from about 70 percent by weight to about 90 percent by weight of water, from about 1 percent by weight to about 10 percent by weight of a dye molecule, from about 2 percent by weight to about 6 percent by weight of a hydroxyethylated polyethyleneimine having incorporated therein from about 65 percent to about 80 percent of hydroxyl substituents, and additive components.
Further, U.S. Pat. No. 4,705,567 discloses heterophase ink compositions which comprise water and a dye covalently attached to a component selected from the group consisting of poly(ethylene glycols) and poly(ethylene imines), which component is complexed with a heteropolyanion. In addition, U.S. Pat. No. 4,267,088 discloses a solvent resistant ink and coating comprising an aqueous solution of epichlorhydrin-modified polyethyleneimine and an ethylene oxide-modified polyethyleneimine. The modified polyethyleneimines are ethoxylated water-soluble polymers formed by the reaction of relatively high molecular weight polyethyleneimines with ethylene oxide. Also, U.S. Pat. No. 4,167,393 discloses a method for binding a water-soluble direct dye to paper by including in the dye a binder such as polyethyleneimine. The polyethyleneimine is generally produced by the polymerization of ethyleneimine in the presence of an acid catalyst, corresponding propyleneimines, and the like. According to the teachings of this reference, branched polyethyleneimines are most preferred, as stated at column 3, lines 31 and 32.
While the above compositions may be suitable for their intended purposes, there continues to be a need for improved ink jet ink compositions. There also continues to be a need for inks that exhibit waterfastness and that are suitable for use in continuous stream ink jet printing processes. In addition, there is a need for economically attractive ink jet inks with acceptable toxicological properties that also enable waterfast prints. Further, there is a need for ink jet inks that enable waterfast prints and that do not result in clogging of the jets. Additionally, there is a need for ink jet inks that contain N-hydroxyl-substituted polyethyleneimines that are compatible with the dyes that are frequently selected for ink jet inks. A need also exists for ink jet inks with low viscosity. There is also a need for ink jet inks with rapid drying times. Additionally, there is a need for ink jet inks that enable generation of high quality images. Further, there is a need for ink jet inks for which the hues remain stable upon drying, so that when images of one color are formed and dried, they will retain their hue when rewetted with a layer of ink of another color during processes such as full color printing. A need also exists for ink jet inks that do not form precipitates with aging.